const symid = Symbol("productno")
interface Product {
    [symid]: number |string
    name: string
    price: number
    account: number
    buy(): string
}

type A = Product["price"]
type B = Product["price" | "name"]
type S = Product[typeof symid]


// typeof 跟着变量  keyof 后面跟着是类型
type PKeys = keyof Product
let pKeys:PKeys = "account"
export {}